1. Field of the Invention
This invention relates to a driving apparatus for driving a magnetic stepping motor to be used as the odometer of a vehicle.
2. Description of the Related Art
In general, a driving apparatus for a magnetic stepping motor (hereinafter referred to as "stepping motor") has a circuit constructed such that signal pulses are applied to a plurality of coils of the motor which are located adjacent to its motor having N and S poles, so as to rotate the rotor at a constant speed. The coils are magnetized in a predetermined order, thereby rotating the rotor at an exactly constant speed. Each of the signal pulses has a rectangular waveform showing a step response, i.e., having an abrupt rise and fall. Thus, the rotor will rotate abruptly in accordance with an abrupt change in the waveform, resulting in occurrence of motor noise.
To reduce the motor noise, a method is considered which varies the voltage waveform of each signal pulse so as to have a gentle rise and fall by interposing capacitors between adjacent coils. In this method, the time required for the change of the voltage waveform is relatively long, which results in a reduction in the motor noise.
However, capacitors to be used as above must be non-polar, and must have a capacitance of several tens .mu. F, inevitably being expensive and large. It is difficult to incorporate a circuit, having such large capacitors, in a small space for a vehicle odometer or the like.